In association with high functionality and multi-functionality of electronic apparatuses in recent years, an amount of information to be exchanged between electronic apparatuses is increased. For example, the electronic apparatus is often coupled to other electronic apparatuses through wired communication. In the case of exchanging a lot of pieces of data, an optical fiber is often used in the wired communication.
In optical communication using an optical fiber, an output level of an optical signal outputted from a transmission device is often controlled. For example, PTLs 1 and 2 each disclose a communication system that controls an output level in a transmission device, based on an input level in a reception device. Moreover, for example, PTL 3 discloses a communication system that controls an output level in a transmission device, based on an error rate measured by a reception device.